Apparatus and method for multicast data packet forwarding

ABSTRACT

A switching device receives a data packet and searches for a layer 3 multicast destination address specified in a header of the received data packet in a layer 3 multicast forwarding database table. The switch searches for a corresponding port list in a layer 3 egress table if the layer 3 multicast destination address is found. However, if the layer 3 multicast destination address is not found, the switch searches for a layer 2 destination address specified in header of the received data packet in a layer 2 multicast forwarding database table, and the switch searches for a port list in a layer 2 egress table if the layer 2 destination address is found. If neither the layer 3 or layer 2 destination address is found in the searches, the switch discards or floods the received data packet out all ports of the switching device.

TECHNICAL FIELD

Embodiments of the present invention relate to data communications. In particular, embodiments relate to using both OSI model layer 2 and layer 3 forwarding database tables in a switching device to make multicast data packet forwarding decisions.

BACKGROUND ART

In data communication networks, multicast data packet routing or forwarding allows a source host to send a data packet to a group of destination hosts without requiring that the source host copy the packet and send each copy individually to each destination in the group. In OSI Model Layer 3 devices (e.g., a data networking router), multicast routing is accomplished, for example, using a group destination Internet Protocol (IP) address in the range of 224.x.x.x to 239.x.x.x for IP version 4 (IPv4), or in the range of FFxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx for IP version 6 (IPv6), as the destination IP address in the IP header of a multicast data packet. In OSI Model Layer 2 devices (e.g., a switch), multicast forwarding is accomplished using a Multicast IEEE 802.3 Media Access Control (MAC) address in the range of 01:00:5E:xx:xx:xx for IPv4, or in the range of 33:33:xx:xx:xx:xx for IPv6, as the destination MAC address in the Data Link header of the multicast data packet.

Layer 2 multicast forwarding may be achieved by configuring a layer 2 multicast Forwarding Database (FOB) table in a layer 2 switch with entries that each specify a particular multicast MAC address, a Virtual Local Area Network (VLAN) identifier (VLAN ID), and a corresponding list of ports on the layer 2 device out which a multicast data packet specifying the multicast MAC address and VLAN is to be transmitted for forwarding purposes. The list of ports may be dynamically learned using the Internet Group Management Protocol (IGMP) (IPv4)/Multicast Listener Discovery (MLD) (IPv6) snooping protocols. The layer 2 FOB table normally includes both unicast MAC address entries and multicast MAC address entries.

Layer 3 multicast data packet forwarding or routing may achieved by configuring a layer 3 multicast FDB table in a switching device with entries that each specify a particular source IP address, a group (or multicast) destination IP address, a VLAN ID, and a corresponding list of ports (along with a list of VLAN IDs for each port) on the switching device out which a multicast data packet specifying the group destination IP address and VLAN ID is to be transmitted. The list of ports may be dynamically learned using the IGMP snooping protocol. The list of VLAN IDs per port may be learned using a layer 3 multicast routing protocol, such as Protocol Independent Multicast (PIM), or Multicast VLAN Registration (MVR).

Note, the switching device may be a layer 2 device or a layer 3 device. In particular, the switching device does not have to be a layer 3 device to utilize the layer 3 table lookups. For example, current switches utilize layer 3 table lookups even when they are performing a layer 2 device role (e.g. IGMP snooping).

Prior art switch and router architectures use either the layer 3 multicast FDB or the layer 2 MAC FDB to provide multicast forwarding to provide both layer 2 multicast data packet forwarding and layer 3 multicast data packet routing. In the prior art, even though a layer 2 FDB table may have sufficient space for storing multicast MAC address entries, the layer 2 FDB table is used only for storing unicast MAC address entries for unicast data packet forwarding.

What is needed is a method and apparatus utilizing both the layer 2 multicast FDB table and the layer 3 multicast FDB table for multicast forwarding and thereby significantly increase the number of available FDB table entries.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be understood more fully from the detailed description given below and from the accompanying drawings of various embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments, but are for explanation and understanding only.

FIG. 1 illustrates an aspect of an embodiment of the invention.

FIG. 2 illustrates an aspect of an embodiment of the invention.

FIG. 3 illustrates an embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the invention use both layer 2 and layer 3 lookup tables in making IP multicast data packet traffic forwarding decisions. With reference to FIG. 1, an embodiment of the invention implements, for example, in conjunction with hardware managed by a multicast manager module, the illustrated egress tables 115, 120 and corresponding cache entries 105, 110. In FIG. 1, boxes 105 and 115 refer also to corresponding layer 3 operations, and boxes 110 and 120 refer to corresponding layer 2 operations. According to one embodiment of the invention, as a first step, a layer 3 multicast FDB table lookup is performed at 105 upon a layer 3 device receiving a layer 3 multicast data packet, e.g., a IP multicast data packet, using the layer 3 (e.g., IP) source address (S), the layer 3 (e.g., IP) destination address (e.g., IP multicast group address (G)), and the VLAN ID (V) from the header of the IP multicast data packet, as input. If the look up is successful, that is, if a matching entry is found, or a “hit” occurs, in the layer 3 cache, an index to the layer 3 egress table 115 is output. However, if there is a miss at layer 3, that is, if the layer 3 multicast data packet is not recognized, then, as a second step, a layer 2 multicast FOB table lookup is performed at 110 using the received packet's destination MAC address (MAC) and VLAN ID (VLAN) as input. If the look up is successful, that is, if a matching entry is found, or a “hit” occurs, in the layer 2 cache, an index to the layer 2 egress table 120 is output. If a miss occurs both at the layer 3 cache and the layer 2 cache, the received packet is dropped (discarded), or dropped and sent to a processor for management functions, or flooded out all ports associated with the VLAN ID (v) specified in the header of the packet.

In one embodiment of the invention, the layer 3 device operates in what is termed herein as a mixed mode of operation, or simply, mixed mode, to denote the device is utilizing both the layer 2 multicast FOB table (cache table 110) and the layer 3 multicast FOB table (cache table 105) for programming the multicast cache entries. In mixed mode, cache entries are programmed in the corresponding layer 3 cache table 105 or the layer 2 cache table 110 depending on the type of multicast packet that is received and the value of the cache type associated with each cache table.

A cache type field associated with each cache table specifies which layer 2 or layer 3 multicast forwarding or routing protocol module initiates adding or deleting a cache entry into which layer 2 or layer 3 cache entry table. For example, if a layer 3 multicast routing protocol (e.g., PIM) module initiated the cache add, a cache entry is programmed in to the layer 3 (L3) cache table 105 given PIM is a cache type that is associated with the layer 3 cache entry table. Likewise, if a layer 2 multicast forwarding protocol (e.g., IGMP snooping) module initiated the cache add, then the cache entry is programmed in to the layer 2 (L2) cache table 110 given IGMP is a cache type that is associated with the layer 2 cache entry table. In one embodiment of the invention, table 1 below provides guidelines for programming multicast FDB entries into an appropriate cache table while operating in mixed mode:

TABLE 1 Cache distribution table Cache Type Cache Table PIM L3 Cache MVR L3 Cache Private VLAN L3 Cache IGMP/MLD SNOOPING L2 Cache

With reference to FIG. 2, an embodiment of the invention determines the multicast FOB table location as follows. If the cache type of the multicast data packet forwarding or routing protocol module that is programming the cache table is a layer 3 (L3) module 205, e.g., PIM, such module coordinates with a multicast manager module 215 to program entries in the layer 3 cache table 105. If, on the other hand, the cache type of the multicast data packet forwarding or routing protocol module that is programming the cache table is a layer 2 (L2) module 210, e.g., IGMP snooping, such module coordinates with multicast manager module 215 to program entries in the layer 2 cache table 110.

The multicast manager module 215, in one embodiment of the invention, coordinates with a hardware abstraction layer 220 to determine the cache type for each cache table and to program the actual entries into the appropriate cache table. Hardware abstraction layer 220 coordinates with hardware layer 225 to create the actual cache entries in the correct cache table, including converting layer 3 multicast information to layer 2 multicast information for programming a cache entry in to the layer 2 cache table when operating in mixed mode and when the cache type is mapped to a layer 2 cache table. In one embodiment, hardware layer 225 includes a software interface to receive messages from hardware abstraction layer 220 to control the hardware for programming the cache entry with the appropriate values of S, G, V, or MAC, VLAN, as the case may be.

With reference to FIG. 3, according to one embodiment of the invention, a layer 3 device's operating system maintains database software for supporting linked lists of software copies of cache entries to be inserted into respective layer 3 or layer 2 cache tables 105 and 110, as appropriate depending on the cache type. In one embodiment, such software executes within hardware abstraction layer 220. In one embodiment, inserting cache entries is accomplished as follows.

-   -   1. A layer 3 multicast (e.g., Internet Protocol multicast         (IPMC)) cache node is created in a list, for example, a linked         list, for each cache add operation requested by a layer 3         multicast routing protocol module, such as a PIM or IGMP         Snooping module. This cache node is a software copy of the cache         entry to be created in the cache table 105 in hardware.     -   2. Depending on the cache type (e.g., PIM or Snoop or MVR), the         IPMC node's cache mode field is set, according to table 1 above,         that is, Cache Mode=L2 or Cache Mode=L3.     -   3. If the IPMC node's cache mode is layer 2 (Cache Mode=L2),         then the IP multicast group address is converted into a layer 2         (MAC) multicast group address and VLAN ID (from inputs S, G, V         (see FIG. 1)) and that information is ultimately used to create         the corresponding cache table entry 110 and egress table entry         120.     -   4. The nodes in the MAC-VLAN cache link list maintain a link         with corresponding IPMC nodes in the IPMC linked list, and vice         versa, for faster lookup operations.

It should be noted that in the above-described operation, the MAC-VLAN nodes are only created if the associated cache entries are to be added to the L2 cache table 110.

In one embodiment of the invention, the database that maintains a linked list of IPMC nodes contains in each node the appropriate corresponding cache information (Source IP address, IP multicast group address and VLAN ID) to create entries in cache table 105, and further contains the information to create corresponding egress VLAN, port lists in table 115.

Additionally, each IPMC node in the list contains flags indicating L2_MODE or L3_MODE to indicate the cache table that is to be programmed with the information in the node to create a cache table entry.

In one embodiment, a multicast group MAC address-ULAN ID database element based on a multicast group MAC address key is created for the entries to be created or inserted into the layer 2 cache table 110. If an entry is to be inserted into the layer 2 cache table, a layer 2 index is allocated instead of a layer 3 index.

With further reference to FIG. 2, the hardware abstraction layer 220, in one embodiment, communicates with hardware layer 225 via a software layer or interface to receive messages from hardware abstraction layer 220 that programs the hardware with a new cache entry with the appropriate values of S, G, V and cache mode set to layer 2 or layer 3 as the case may be. The software layer processes each message, determines if the cache mode=L2, and if so, then converts the IP multicast group address to a MAC multicast group address and programs the layer 2 cache table accordingly. If, on the other hand, the cache mode=L3, the software layer programs the layer 3 cache table using the inputs S, G, V derived from the received packet, as described above.

In one embodiment of the invention, static FDB configuration allows the creation of FDB entries for multicast MAC addresses using, for example, a command line interface (CLI) command. These entries are also inserted in the layer 2 cache table and are used for hardware-based packet forwarding. In one embodiment, if there is a conflict between a learned, dynamic, <MAC,VLAN> entry created by the Multicast Manager Module 215 and a static entry inserted by an FDB manager module, the static entry takes precedence and the dynamic entry is deleted in the hardware table.

In one embodiment of the invention, when IP multicast group address forwarding entries are using the layer 2 cache table, the multicast entries are inserted as static entries in the table to avoid undesirable interactions with layer 2 protocol- or user administered-FDB flushing. These layer 2 multicast entries may also take precedence over dynamic layer 2 unicast entries, in one embodiment.

In one embodiment of the invention, a switching device receives a data packet, searches for a layer 3 multicast destination address specified in a header of the received data packet in a layer 3 multicast forwarding database table, and searches for a corresponding port list in a layer 3 egress table if the layer 3 multicast destination address is found. If the layer 3 multicast destination address is not found, the device searches for a layer 2 destination address specified in a header of the received data packet in a layer 2 multicast forwarding database table, and searches for a port list in a layer 2 egress table if the layer 2 multicast destination address is found. The device discards the received packet or floods the received packet out all ports of the switching device if the layer 3 multicast destination address is not found and the layer 2 multicast destination address is not found.

In one embodiment, the layer 3 multicast destination address is an Internet Protocol multicast destination address. In yet another embodiment, searching for a layer 3 multicast destination address specified in a header of the received data packet in a layer 3 multicast forwarding database table further comprises additionally searching for a layer 3 source address specified in the header of the received data packet in the layer 3 multicast forwarding database table.

In one embodiment, a first index to a layer 3 egress table is returned if the layer 3 multicast destination address is found, and searching for a corresponding port list in a layer 3 egress table if the layer 3 multicast destination address is found comprises searching using the first index for a corresponding port list in a layer 3 egress table if the layer 3 multicast destination address is found.

In one embodiment, if the layer 3 multicast destination address is not found, the device searches for a multicast MAC address specified in a header of the received data packet in a layer 2 multicast forwarding database table. In another embodiment, if the layer 3 multicast destination address is not found, the device additionally searches for a virtual local area network identifier (VLAN ID) specified in the header of the received data packet in a layer 2 multicast forwarding database table.

In one embodiment, a second index to a layer 2 egress table is returned if the layer 2 multicast destination address is found, and that index is used to search for a port list in a layer 2 egress table if the layer 2 multicast destination address is found.

In the above description, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known structures and techniques have not been shown in detail in order not to obscure the understanding of this description. Those of ordinary skill in the art, with the included descriptions, will be able to implement appropriate functionality without undue experimentation.

References in the specification to one “embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

Embodiments of the invention as discussed above may be implemented as a series of software routines executed by computer system. The software routines may comprise a plurality or series of instructions, code sequences, configuration information, or other data to be accessed and/or executed by a processing system such as one or more processors. Initially, the series of instructions, code sequences, configuration information, or other data may be stored in data storage and transferred to memory via a bus. It is to be appreciated that the series of instructions, code sequences, configuration information, or other data can be stored in a data storage using any conventional computer-readable or machine-accessible storage medium, such as a diskette, CD-ROM, magnetic tape, DVD, ROM, etc. The instructions, code sequences, configuration information, or other data may be copied from the data storage, such as mass storage, and accessed and executed by a processor.

In alternate embodiments, the present invention is implemented in discrete hardware or firmware. For example, one or more application specific integrated circuits (ASICs) could be programmed with some or all of the above-described functions of the present invention.

Accordingly, embodiments of an invention that improve multicast data packet forwarding are described. From the foregoing description, those skilled in the art will recognize that many other variations of the present invention are possible. Thus, the present invention is not limited by the details described. Instead, the present invention can be practiced with modifications and alterations within the spirit and scope of the appended claims. 

The invention claimed is:
 1. In a switching device, a method comprising: receiving a data packet; searching for a layer 3 multicast destination address specified in a header of the received data packet in a layer 3 multicast forwarding database table; searching for a corresponding port list in a layer 3 egress table if the layer 3 multicast destination address is found; if the layer 3 multicast destination address is not found, searching for a layer 2 destination address specified in a header of the received data packet in a layer 2 multicast forwarding database table; and searching for a port list in a layer 2 egress table if the layer 2 multicast destination address is found; and performing an action on the received data packet if the layer 3 multicast destination address is not found and the layer 2 multicast destination address is not found, the action being one of: discarding the packet, flooding the packet out all ports of the switching device excluding the port on which the packet was received, or sending the packet to a processor for further processing or learning.
 2. The method of claim 1, wherein the layer 3 multicast destination address is an Internet Protocol multicast destination address.
 3. The method of claim 1, wherein searching for a layer 3 multicast destination address specified in a header of the received data packet in a layer 3 multicast forwarding database table further comprises additionally searching for a layer 3 source address and VLAN ID specified in the header of the received data packet in the layer 3 multicast forwarding database table.
 4. The method of claim 1, further comprising providing an index to a layer 3 egress table if the layer 3 multicast destination address is found; and wherein searching for a corresponding port list in a layer 3 egress table if the layer 3 multicast destination address is found comprises searching using the index for a corresponding port list in a layer 3 egress table if the layer 3 multicast destination address is found.
 5. The method of claim 1, wherein if the layer 3 multicast destination address is not found, searching for a layer 2 destination address specified in a header of the received data packet in a layer 2 multicast forwarding database table comprises searching for a multicast MAC address specified in a header of the received data packet in a layer 2 multicast forwarding database table.
 6. The method of claim 1, wherein if the layer 3 multicast destination address is not found, searching for a layer 2 destination address specified in a header of the received data packet in a layer 2 multicast forwarding database table comprises additionally searching for a virtual local area network identifier (VLAN ID) specified in the header of the received data packet in a layer 2 multicast forwarding database table.
 7. The method of claim 1, further comprising providing an index to a layer 2 egress table if the layer 2 multicast destination address is found, and wherein searching for a port list in a layer 2 egress table if the layer 2 multicast destination address is found comprises searching using the index for a port list in a layer 2 egress table if the layer 2 multicast destination address is found.
 8. An apparatus comprising a non-transitory computer-readable medium containing a set of executable instructions that when executed by a switching device causes a switching device to: receive a data packet; search for a layer 3 multicast destination address specified in a header of the received data packet in a layer 3 multicast forwarding database table; search for a corresponding port list in a layer 3 egress table if the layer 3 multicast destination address is found; if the layer 3 multicast destination address is not found, search for a layer 2 destination address specified in a header of the received data packet in a layer 2 multicast forwarding database table; and search for a port list in a layer 2 egress table if the layer 2 multicast destination address is found; and perform an action on the received data packet if the layer 3 multicast destination address is not found and the layer 2 multicast destination address is not found, the action being one of: discarding the packet, flooding the packet out all ports of the switching device excluding the port on which the packet was received, or sending the packet to a processor for further processing or learning.
 9. The apparatus of claim 8, wherein the layer 3 multicast destination address is an Internet Protocol multicast destination address.
 10. The apparatus of claim 8, wherein the search for a layer 3 multicast destination address specified in a header of the received data packet in a layer 3 multicast forwarding database table further comprises an additional search for a layer 3 source address and VLAN ID specified in the header of the received data packet in the layer 3 multicast forwarding database table.
 11. The apparatus of claim 8, wherein the non-transitory computer-readable medium further contains a set of executable instructions that when executed by the switching device causes the switching device to provide an index to a layer 3 egress table if the layer 3 multicast destination address is found; and wherein the search for a corresponding port list in a layer 3 egress table if the layer 3 multicast destination address is found comprises a search using the index for a corresponding port list in a layer 3 egress table if the layer 3 multicast destination address is found.
 12. The apparatus of claim 8, wherein if the layer 3 multicast destination address is not found, the search for a layer 2 destination address specified in a header of the received data packet in a layer 2 multicast forwarding database table comprises a search for a multicast MAC address specified in a header of the received data packet in a layer 2 multicast forwarding database table.
 13. The apparatus of claim 8, wherein if the layer 3 multicast destination address is not found, the search for a layer 2 destination address specified in a header of the received data packet in a layer 2 multicast forwarding database table comprises an additional search for a virtual local area network identifier (VLAN ID) specified in the header of the received data packet in a layer 2 multicast forwarding database table.
 14. The apparatus of claim 8, wherein the non-transitory computer-readable medium further contains a set of executable instructions that when executed causes the switching device to provide an index to a layer 2 egress table if the layer 2 multicast destination address is found, and wherein the search for a port list in a layer 2 egress table if the layer 2 multicast destination address is found comprises a search using the index for a port list in a layer 2 egress table if the layer 2 multicast destination address is found. 